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About Landsat 5, 7, 8 & Sentinel-2 Atmospheric Correction / Conversion to Surface Reflectance (SR) Tutorials & Courses

The links in the above SR Tutorials drop-down menu take you directly to Atmospheric Correction/SR tutorials or courses in order to convert to SR independently. Landsat can be downloaded in SR format as is explained in next paragraph. Sentinel-2 can only be downloaded in top of atmosphere (TOA) format, but a free toolkit is available online that can be used to convert Sentinel-2 to SR (explained more below).

IF YOU PREFER, YOU CAN ORDER LANDSAT FROM THE USGS ALREADY CONVERTED TO SR; keep in mind that USGS Landsat 8 Algorithm SR is not purely a DOS method (subtracting USGS SR from USGS TOA will result in variable values). To order SR imagery, open Data Sources folder on the left and access EarthExplorer; in Data Sets, open Landsat then access Landsat Collection 1 Level-2 (On-Demand) (that is SR). Click the following links for Landsat SR background information: Landsat Level-2 Science Products & Landsat Collections Tier Information (both USGS offsite pages that open in new tabs). You need an account to order USGS SR imagery (free and easy process). USGS SR is in an integer raster format; divide by 10,000 to convert to surface reflectance units. The USGS will email you a link to download the data when it is ready.

Tutorials and Courses on this website guide you through the process of converting imagery to SR (tutorials are designed for ArcGIS and QGIS, but may be applied in large part to other GIS software). Conversion to SR here is based on dark object subtraction (DOS; Chavez [1988 and 1996]), which is a well-documented and established method, and applies continuous relative scatter (suggested by Chavez [1988]) developed here. Learn about DOS here.

Landsat 8 SR includes the GIS Ag Maps Landsat 8 DOS Surface Reflectance Method applying the Lowest Valid Value Attribute Table method which has been cited in numerous publications, including Remote Sensing of Environment (includes results). (The current scatter table has slightly different values as that used in the article, but the original table remains accessible; we do recommend using the current table as is explained in tutorials). Other methods have been developed to establish scatter that involve viewing the histogram, and are described through links above. ArcGIS or free QGIS can be used to convert to SR.

Landsat 5 and 7 SR is based on the one-percent dark object subtraction (DOS; Chavez [1988 and 1996]) COST Method (Chavez, 1996), which is a well-documented and established method for Landsat 5 & 7 (access the Chavez [1996] article here for details and results; PDF on this website). Continuous relative scatter (suggested by Chavez [1988]) is applied to Landsat 5 and 7 here, where the power correlation between band center wavelength and scatter has the proper value of R² = 1.0 (Chavez, 1988). Power exponents also have the proper range of values based on Chavez (1988) and research completed here. This is explained in more detail in the tutorials. Relative scatter for Landsat 5, 7, 8, and Sentinel-2 are based on values that all fit together with a correlation between band center wavelength and scatter reflectance of R² = 1.0. Relative scatter tables are designed to start with red band for the specific satellite, but the starting band can be any visible band that you feel is appropriate (explained more in tutorials).

Sentinel-2 SR is based on the GIS Ag Maps Sentinel-2 DOS Surface Reflectance Method. Sentinel-2 is downloaded in top of atmosphere (TOA) integer units, which is good because it eliminates a step in the SR conversion process. Methods to establish scatter using the ArcGIS Attribute Table of QGIS histogram (QGIS cannot generate a raster attribute table) are explained in courses and tutorials. Sentinel-2 cannot be downloaded in SR format which is considered Level-2A, but there is a free online toolbox that can be installed that can be used to convert to SR (Level-2A, also known as Bottom of Atmosphere reflectance). The following page can be used to access the toolbox: ESA Sentinel-2 Level 2A Toolbox (offsite ESA page; opens in new tab).

 

 References

Chavez, P.S., Jr. 1996. Image-based atmospheric corrections–revisited and improved. Photogrammetric Engineering and Remote Sensing 62(9): pp.1025-1036.

Chavez, P.S., Jr. 1988. An improved dark-object subtraction technique for atmospheric scattering correction of multispectral data. Remote Sensing of Environment 24: pp.459-479.